Method of burning mineral substances and porous product thereof



ay 3, 1938. E, L UNDMAN 2,,M6,030

METHOD OF-BURNING MINERAL SUBSTANCES AND POROUS PRODUCT THEREOF Filed Aug. 21, 1936 Patented May af ioss METHOD ornunmc mums]. sunronous monuc'r sTANcEs AND THEREOF Emrlk Ivar Lindinan, Stocksnnd, near Stockhelm, Sweden Application August 21,1936, Serial No. 97,272 In Sweden December 15. 1984 eclaim. (oi. ass-s2) Certain mineral substances may to a porous clinker-like product by being heated at a continuously increasing temperature, first rather quickly to a temperature near the melting 5 point; and then continuously to such a temperature that the material assumes a thorough or substantially thorough viscous melting consistency to facilitate the expansion of the material by the gases enclosed in the raw materialor ma terials. In this viscous state of beginning .of

. melting the material is highly sticky and for this be expanded reason it has been necessary to carry out the process in an ordinary tunnel furnace or in a tunnel furnace having a substantially circular path for the cars. Then the material is shaped to bodies (blocks, bricks etc.) having a shape suitable for a rapid absorption of heat. Such bodies are placed loosely on a table or car which is moved through the furnace in a straight or substantially circular path. In some cases a pulverized fuel may be admixed with the mineral material. When the whole mass has reached the state mentioned above the heating is stopped.

- nary clay, may be dumped from cars 20 into a On account of the sticky and glutinous consistency of the mass, the process could not heretofore be carried out in a burning chamber.

The chief purpose of this invention is to render furnace having a rotary it possible to carry out such burning process in 3 a furnace having a rotary or rockable burning chamber, while using a flame burning within said chamber above the material to be melted.

A further object of this invention is to cool the wall' of the furnace locally so as to prevent the sticky expanding material from adhering to the wall.

, A further object of this invention is to build the wall of such a furnace, having a rotary or rocking motion of its chamber, of a material hav- Y ing a coefflcient of heat transmission substantially higher than that of the expanding material.

A further object is to produce such clinker-like product at a cost substantially lower than was heretofore possible. Further objects will be evident from the following specification and claims.

One embodiment of a plant for carrying out the method in accordance with this invention is illustrated in the annexed drawing in which Fig. 1 shows an elevation of the shows a cross-section through the furnace proper, on the line II-II in Fig. l and on a larger scale. Referring now to the drawing l indicates the cylindrical metal wall of the furnace which is rotated or rocxed in well-known manner. The

plant, while Fig. 2

hopper 2| discharging into the upper end of the rotary furnace I. Said upper end is enclosed in a stationary hood 22, from which a pipe 23 for the gases of combustion leads to a chimney-stack 24. The furnace cylinder rests on rollers '25 and -.is rotated or rocked in well-known manner, for instance, by use of an electric motor M driving the furnace through one or more toothed gearings G. The lower end of the rotary furnace cylinder I is enclosed by a stationary casing 26, through which one or more burners 6 for gas, oil, pulverized coal or the like extend into the furnace cylinder. I

From the casing 28 a hopper 21 for the burned material discharges into the cooling rotary cylinder 28, running on rollers 29 and driven by an electric motor 30. From the cooling cylinder 28 the material is fed into a crushing machine 3|. 20 The lower hot and of the furnace l. is cooled by means of water sprayed on its outer side from water jets l0. A flange 32 on the cylinder I prevents the water from flowing into the casing 26. From the chimney-stack 24 a return'pipe 33 for the gases of combustion leads back to a pipe 35, to which also a pipe 36 leads from the atmosphere. In the pipe 35, which extends through the casing 26 into the furnace I, a fan 31 is provided to blow gases into the furnace I. Into the pipe 35 also a hopper 38 discharges via a valved pipe. Valves are also provided in the pipes 35 and 36.

I As illustrated in Fig. 2 the wall I of the furnace is lined with a refractory material 2, such as chamotte, which must have a higher coemcient of heat transmission than that of the charge 3, when the latter is being expanded. The charge consists of clay, by preference, quaternary, and/or certain rocks, preferably eruptive, to which other 4 materials may be admixed or not. The charge is heated by means of a hot flame 4 from the burner 6, The flame is directed towards the surface of the charge in the centre of the furnace, but the flameshould not come into contact with the furnace walls. The flame is displaced somewhat upwards, in relation to the axis of the furnace so that the flame has a greater distance from the to the furnace wall at the point C or within the zone C-D, even when the charge assumes a thoroughly, viscous state of beginning (initial) melting and for this reason has acquired an extremely sticky and glutinous state.

The inner wall 2 of the furnace is made of a material having a coefficient of heat transmission substantially higher than that of the expanding charge, so as to effect a sufficient absorption of heat from the lower surface of the charge.

The necessary cooling may be effected in several different ways, separately or in combination. Thus, the furnace wall may be kept cold by a cooling action so that said wall absorbs a sufficient quantity of heat from the surface of the charge and thus causes said surface to lose its stickiness as a result of the lowering of the temperature, before it reaches the point C of contact during the rolling motion of the charge. Furthermore, within the zone C-D the wall must be able to absorb, from that portion of the surface of the charge, which is in contact with the wall, such an additional quantity of heat that said surface of the charge remains so cold within the zone C-D that it cannot stick to the furnace wall.

Such cooling of the wall may be attained in several different ways. A simple method is to cool it by spraying water directly on the outside thereof by means of the sprayers I0. Cooling coils l I, Fig. 2, may be placed in the walls, but in practice this method is somewhat expensive and cumbersome. 1

The furnace wall may, however, also be cooled on its inner side. In a rotary furnace of this type the free (that is, uncovered) portion of furnace lining is subjected to a very strong radiation of heat from the flame and. for this reason accumulates heat, which in ordinary cases is then given to the charge by radiation or direct convection. In accordance with this invention this effect may be avoided by cooling the furnace wall from the inside by means of a current of relatively cold air or other gas, which is pressed in between the flame and the furnace wall through the pipe 35. This cold current of air shields the furnace wall against the radiating heat, that is, absorbs at least a considerable part of it, before it can reach the furnace wall; and simultaneously the cold current of air or gas directly absorbs heat from the surface of the furnace wall. The heat absorbed by the gas current is not lost but may be used for pre-heating the raw material in the upper art of the furnace I. For this purpose, however, it is preferred to use the gases of combustion from the furnace, after they have been cooled sufficiently by pre-heating the cold raw material in the upper part of the furnace I. The gases thus cooled are returned through the pipe 33 to the pipe 35 and blown into the furnace I. The high contents of carbon dioxide of such gases of combustion renders their shielding action very high. The proportion of fresh air and gases of combustion supplied through the pipe 35 may be controlled by means of the valves in the pipes 33 and 35. In many cases a combined external and internal cooling is convenient, though, of course, the internal cooling gives the best economy of heat.

If finely divided cold raw material of suitable fineness is available, it may be advantageous to introduce it through the hopper 38 into the current of air or gas in the pipe 35 so that said cold raw material is supplied to the charge in the zone BC. The same raw material as that of the but in some cases it may be advantageous to use another raw material. If the charge or principal material 3 to be burnt consists of wet clay, a finely crushed rock. may be introduced into the current of air or gas as a cooling agent. The two materials will then together constitute the expanded final product.

When clay and rocks are burned in a rotary or rocking furnace in accordance with this invention, it is possible to get coherent lumps or cylindric bodies of a length of several meters, which consist of an expanded molten mass; and such bodies do not stick to the furnace wall. The process of this invention is substantially based upon the new observation that the raw material or materials have a high power of heat conduction during the heating process until the expansion is carried out by means of gases evolved or enclosed in the material. As this expansion proceeds the power of heat conduction of the expanding mass rapidly decreases. As its voluminar weight (weight per unit of volume) is decreased'due to the expansion, the quantity of heat per unit of volume of the material is decreased, though the temperature remains unaltered. For this reason it is possible to effect that surface-cooling of the material within the zone BC which is necessary to cause the surface of the material to loose its stickiness. It is to be observed that the expanding material has a substantially reduced power of heat conduction, and therefore, the cooling is limited to a surfacelayer and does not penetrate deep into the mass, while simultaneously the inner furnace-wall has a substantially higher power (or coeflicient) of heat transmission than that of the expandin material. By means of the combined heating and cooling steps according to this invention the mass being treated, which is heated to such a high temperature that it is viscous as glue and extremely sticky, may be caused to roll on a furnace-wall of chamotte or other refractory material without adhering thereto, though in the processes heretofore known the material would adhere and stick to the furnace wall so firmly that the furnace chamber would be obturated by the viscous sticky material after a very short period of operation.

The product obtained by the process of this invention is taken out of the furnace in suitable manner for instance, through the hopper 21 and the cooling drum 28 after the burning is finished. If this product is crushed in the crusher 3i it shows the same cellular structure as if the material had been burnt on cars in a tunnel furnacc. The cellular clinker-like product of this invention is very useful for various kinds of light concrete for walls insulating against heat and sound. It is especially useful for fire-resistant constructions and for carcass floorings to insulate against sound. The material is much cheaper than that produced in a tunnel furnace but is quite equivalent to the same in all other respects. Thus, the material produced in accordance with this invention has very different moduli of elasticity in the individual pieces, when crushed. Slabs, walls, etc. produced by use of such crushed material have, therefore, an exceptionally high insulation against sound, because in its passage through pieces of very different moduli of elasticity in the concrete the sound is highly damped and absorbed.

The raw materials used in accordance with this charge being burnt in the furnace may be used, invention are such mineral substances which may be sintered and in which a sufficient quantity of gases are liberated, when the materials are heated to attain a viscous state, to expand the mass to a porous cellular product. The gases may be evolved at the heating and/or may be enclosed or dissolved in the mineral substances. :As an example of such mineral substances the following may be mentioned: various schists or slates. also of an eruptive origin, and other eruptive rock's, such as fine-grained granite, basalt, diabas, and also certain clays and clayey substances, such as quaternary clay. Mixtures of such substances may also be used as raw material in accordance with this invention but quartz does not yield a sufficient quantity of gases and cannot be used. Certain admixtures of substances poor in gas may be made, but the mixed compound mass, when burned, shall evolve or liberate the gas necessary for a satisfactory expansion in the viscous state of the mass being sintered. The term mineral material or substance capable of expansion by gas liberated therein at sintering temperatures" in the specification and claims should be interpreted to cover such masses, whether compound mixtures or not. The term rotary furnace chamber" also covers a rockable furnace chamber, effecting reciprocating rotary motions of less than a whole revolution.

What I claim is:-

1. A method of manufacturing a cellular clinker-like product, comprising. heating a mineral material capable of expansion by gas liberated therein at sintering temperatures to such a high temperature that the entire mass reaches a viscous substantially thoroughly melting state, by means of a flame burning above said material while in contact with .a supporting wall which moves relative to the material, and is composed of a material having a coeiiicient of heat transmission substantially higher than that of the mass, which is expanded by means oi gases evolved from the material, cooling said mass on its surface in the part thereof that immediately thereafter comes into contact with the furnace wall, to prevent the mass from sticking to said wall, and stopping the heating when the expansion of the material is completed. 7 p

2. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral material capable of expansion by gas liberated therein at sintering temperaturesto such a high temperature that the entire mass reachesa viscous substantially thoroughly melting state, by means of a flame burning above said material while in contact with a relatively rotationally moving supporting wail consisting of a material havinga coefiicient of heat transmission sub,-

stantially higher than that of the mass, which is expanded by means of gases evolved from the material,, cooling the supporting wall to cause it to absorb heat from the adjacent surface of the mass in contact and coming into contact with the cooled wall, to prevent the mass from adhering to said wall, and stopping the heating when the expansion of the material is completed.

3. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral material capable of expansion by gas liberated therein at sintering temperatures to such a high temperature that the entire mass reaches a viscous substantially thoroughly melting state, by means of a flame burning above said material while in contact with a relatively rotationally moving supporting wall consisting of a substance having a coemcient of heat transmission substantially higher than that of the mass, which is expanded by means of gases evolved from the material itself, cooling the supporting wall by sprayin: water on the outer side thereof to cause the wall to absorb-heat from the adjacent surface of the mass in contact and coming into contact therewith, and stopping the heating when the expansion is finished 4. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral material capable of expansion by gas liberated therein at sintering temperatures to such a high having a coeiiicient of heat on sub-' stantlally higher than that of the mass, which is expanded by means of gases evolved from the material itself, cooling the wall by blowing a current of relatively cold gas between said wall and said flame, and cutting 03 said flame when the expansion is finished.

5. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral mass capable of expansion by gas liberated therein at sintering temperatures to such a high temperature that the entire mass reaches a viscous substantially thoroughly melting state, by means of a flame burning above said mass while in contact with a relatively rotationally moving supporting wall consisting of a material having a coefficient of heat transmission substantially higher than that of the mass. which is expanded by means of gases liberated in the mass itself, blowing a current of gas between said wall and said flame, introducing finely divided cold minera1 material into said current to cause said cold material to deposit on that portion of the surface of the material which is about to come into contact with the wall, and stopping the heating when the expansion is finished.

6. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral mass capable of expansion by gas liberated therein at sintering temperatures to such a high temperature that the entiremass reaches a viscous substantially thoroughly melting state, by means of a flame burning above said mass while in contact with a relatively rotationally moving supporting wall consisting of a material having a coefllcient oiheat transmission substantially higher than that of the mass. which is expanded by means of gases liberated in the mass itself, removing the gases of combustion from the zone of treatment, cooling said gases, blowing said cooled gases of combustion in between the flame and the wall to cool the wall, and stopping the heating when the expansion of the mass is complete.

7. A method of manufacturing a cellular clinker-like product, comprising, heating a mineral mass capable of expansion by gas liberated therein at sintering temperatures to such a high temperature that the entire mass reaches a viscous substantially thoroughly melting state, by means of a flame burning above said ing the gases of combustion thus cooled in between the flame and the wall adjacent to that zone thereof which immediately thereafter comes into contact with the mass, and stopping the heating when the mass has been sufliciently expanded.

8. A process of manufacturing a cellular clinker-like material, comprising, heating a mineral mass capable of expansion by gas liberated therein at sintering temperatures at continuously increasing temperatures first rather quickly to a temperature near the melting point and then continuously to a temperature at which the mass substantially thoroughly assumes a highly viscous melting consistency to effect the expansion of the mass by the gases therein, said heating being carried out by means of a flame burning above the mass while the mass is supported on a relatively rotationally moving wall consisting of a material having a coemcient of heat transmission substantially higher than that of the mass, under expansion, cooling said mass on its surface in that part thereof which immediately thereafter comes into contact with the moving wall, to prevent the mass from sticking to said wall, and stopping the heating when the expansion is completed.

9. A cellular, inexpensive, clinker-like product manufactured by heating a mineral mass capable of expansion by gas liberated therein at sintering temperatures at continuously increasing temperatures first rather quickly to a temperature near the melting point and then continuously to a temperature at which the mass substantially thoroughly assumes a highly viscous melting consistency to effect the expansion of the mass by the gases therein, said heating being carried out by means of a flame burning above the mass while the mass is supported on a relatively rotationally moving wall consisting of a material having a coefficient of heat transmission substantially higher than that of the mass, under expansion, cooling said mass on its surface in the part thereof that immediately thereafter comes into contact with the furnace wall, to prevent the mass from sticking to said wall, and stopping the heating when the expansion is completed.

EMRIK IVAR LINDMAN. 

